1. Field of the Invention
The present invention relates to incendiary compositions. More particularly, the incendiary composition of the present invention contains a paraffin wax as a binder to improve ESD sensitivity of titanium/boron/polytetrafluoroethylene compositions. Most particularly, the paraffin wax is present in amounts of from about 5% to about 20%.
2. Brief Description of the Related Art
Reducing the electrostatic discharge sensitivity (ESD) for dry metals is particularly important in the manufacture of incendiary devices. Highly reactive metals provide an excellent source for high burn temperatures, however, the more reactive the metal powders are, the more ESD sensitive they become. ESD sensitive metal powders are likely to ignite during handling or mixing, increasing hazards to personnel and manufacturing equipment.
Combinations of titanium and boron potentially possess extremely high ESD sensitivity, with ignition of approximately 0.0084 joules possible. Other types of metallic mixtures that are less ESD sensitive, such as iron oxide and aluminum, i.e., Thermite, burn too quickly and with relatively low flame temperatures. Some combinations of magnesium, teflon and Viton A, i.e., MTV, high a high flame temperature, but they don""t have the slow burning rate.
In view of the foregoing, there is a need for improved incendiary compositions having a reduced burning rate, low ESD sensitivity and high flame temperature. The present invention addresses this need.
The present invention includes a high temperature incendiary composition comprising a reactive material of titanium, a second reactive material of boron, an oxidizer of polytetrafluoroethylene in an amount of from about 20 weight percent or greater of the composition and a binder of paraffin wax in an amount of from about 5 weight percent to about 20 weight percent, wherein the ratio of titanium to boron ranges from about 81/19 to about 69/31.
Additionally, the present invention includes a high flame temperature product from the process comprising the steps of providing a composition of titanium, boron, polytetrafluoroethylene in an amount of from about 20 weight percent or greater of the composition and paraffin wax in an amount of from about 5 weight percent to about 20 weight percent, wherein the ratio of titanium to boron ranges from about 81/19 to about 69/31 and igniting the composition.
The present invention provides an incendiary composition having a slow burn rate and high flame temperature that is safer to handle and mix because of a reduced sensitivity to ESD.
The present invention relates to incendiary compositions with improved electrostatic discharge (ESD) sensitivity. The incendiary compositions contain a paraffin wax binder to improve ESD sensitivity of titanium, boron and polytetrafluoroethylene composition mixtures. The incendiary compositions are safe to handle, ignite readily, burn at a low and controlled rate and produce a very high flame temperature.
Safe ESD for manufacture and handling of the present invention is in a range greater than 0.023 joules. The human body is capable of producing up to approximately 0.0084 joules. The high temperature incendiary composition of the present invention contains a reactive material of titanium, a second reactive material of boron, an oxidizer of polytetrafluoroethylene, which further includes a binder of paraffin wax that increases the ESD resistance for the titanium/boron/polytetrafluoroethylene combination to a value of more than 0.023 joules and a burning rate of from about 1.0 inch per minute or less.
The composition preferably comprises fine or integrated mixtures of the titanium and boron metals, rather than mere individual aggregates, granules or pellets of the separate metals. The metals are preferably pure form, containing no oxides or other chemical forms. On ignition, the titanium and boron react exothermically together to result in intermetallic compound with a heat energy release of from about 1000 calories per gram. As the purity of the two metals increase, the energy release from the exothermic reaction also increases. Impurities promote side reactions, create stoichiometric imbalances, and dissipate released energy.
Calculations show the mixture of the two reactive metals or titanium and boron forms an intermetallic compound together upon ignition. Solid titanium and boron react to form a liquid, i.e., molten, intermetallic compound, indicated by the formula:
Ti+2Bxe2x86x92TiB2
Other by-products occur, most significantly with the reaction of boron with polytetrafluoroethylene, and the reaction of the paraffin wax with titanium.
The titanium preferably comprises a particle size of from about 44 microns to about 150 microns, with ESD sensitivity increasing to unsafe levels below from about 44 microns and burn rates increasing beyond a slow burn rate above a particle size of from about 150 microns. Particle sizes from about 200 microns provide a burning rate of approximately 4.7 inches per minute or 321 grams per minute. Appropriate particle sizes for the titanium within the particle size range of from about 44 microns to about 150 microns may be used as determined by those skilled in the art for a given purpose in light of the disclosure herein. Boron particles may include any acceptable size, such as from about 0.5 microns to about 1 micron in size, as determined by one of ordinary skill in the art. The chemicals are commercially available in finely divided powders. Titanium powder metal is available from Atlantic Equipment Engineers of Bergenfield, N.J. under the catalog number TI-109 having a purity of approximately 99.7%. Boron is available from Callery Chemical Company of Pittsburgh, Pa. under the tradename SB 95 having from about 95% to about 97% boron and from about 5% to about 3% magnesium oxide (MgO) or SB 90 having from about 90% to about 92% boron and from about 10% to about 8% magnesium oxide (MgO), with both products having an amorphous state with an average particle size of approximately 0.6 microns.
The weight ratio amount of titanium to boron needed for a high flame temperatures ranges from about 81/19 to about 69/31. Preferably within this range, the titanium and boron are present in the composition in substantially stoichiometric proportions for forming the intemetallic compound. As the ratio of titanium to boron decreases, the combination metal becomes increasingly more difficult to ignite, with the proper ratio of titanium to boron for a given incendiary composition determinable by those skilled in the art in light of the disclosure herein.
The incendiary composition includes an oxidizer of polytetrafluoroethylene, also known as Teflon(copyright), in an amount of from about 20 weight percent or greater of the composition. Preferred amounts of polytetrafluoroethylene range from about 20 weight percent to about 30 weight percent, with more preferred amounts of polytetrafluoroethylene ranging from about 20 weight percent to about 25 weight percent. The particles of the polytetrafluoroethylene may be any suitable size, such as from about 20 microns to about 450 micron, with little affect on the burning rate or slag percentage. For example, a polytetrafluoroethylene particle size between 20 microns and 450 microns in a given composition may vary in burning rates between from about 163 grams per minute to about 161 grams per minute with a slag percentage varying between from about 36% to about 40%. As the amount of polytetrafluoroethylene increases, the reaction energy of the titanium/boron ignition decreases, with the proper amount of polytetrafluoroethylene for a given incendiary composition determinable by those skilled in the art in light of the disclosure herein. Polytetrafluoroethylene is available from E. I. duPont de Nemours and Company of Wilmington, Del. under the tradenamexe2x80x94Teflon(copyright) 7C.
The paraffin wax binder is included within the incendiary composition in an amount of from about 5 weight percent to about 20 weight percent. Preferred amounts of paraffin wax range from about 5 weight percent to about 15 weight percent, with more preferred amounts of paraffin wax ranging from about 5 weight percent to about 10 weight percent. Paraffin wax has a melting point of from about 73xc2x0 C. to about 80xc2x0 C., permitting ease of handling. Other waxes of similar characteristics, preferably with at least as high melting point, such as from about 80xc2x0 C. or greater, i.e., 83xc2x0 C., may be used in place of the paraffin wax binder. This permits storage and handling in areas with limited or uncontrolled environments, i.e., storage compartments on ships. As the amount of paraffin wax increases, the flame temperature and burning rate decrease, with the proper amount of paraffin wax for a given incendiary composition determinable by those skilled in the art in light of the disclosure herein. Paraffin wax is available from Aldrich Chemical Company, Inc. of Milwaukee, Wis. under catalog #411671, high temperature paraffin wax with a melting range of from about 73xc2x0 C. to about 80xc2x0 C.
The incendiary composition may be manufactured in a safe manner by decreasing the electrostatic discharge hazard during handling and mixing. The preferred method for preparing the composition of the present invention includes adding the non-binder components, i.e., titanium, boron, an polytetrafluoroethylene, into a bowl before mixing. After the component powders are added, the electrostatic field (E-field) is measured. A commercially available electrostatic fieldmeter is used and measurement is determined according to the manufacturer""s directions. E-field measurements of 3 kilovolts per inch or less permit the method to proceed, with the addition of the paraffin wax. Prior to adding the paraffin wax, the paraffin wax is pre-softened with toluene, or other suitable solvent such as benzene, chloroform, warm alcohol and other like solvents, with the proper selection of solvent determinable by one skilled in the art. Once the paraffin wax has been added, the components are mixed for a total of approximately two and one-half hours. Every halfhour, during the first two hours, the mixing is stopped and the blades and sides of the bowl are scrapped with a conductive spatula. During the last half-hour, the temperature of the mixture is increased from about 90xc2x0 F. to about 140xc2x0 F. by circulating hot water through the mixing bowl, and a stream of air and/or a vacuum is used to remove the solvent.
A high flame temperature product results with the ignition of the incendiary composition of the 81/19 to 69/31 ratio of titanium and boron, 20 weight percent or more polytetrafluoroethylene and 5 weight percent to 20 weight percent paraffin wax. Temperatures of the incendiary composition igniting may range from about 3500xc2x0 F. or higher, with temperatures from about 4000xc2x0 F. to about 5000xc2x0 F. possible, such as approximately 4500xc2x0 F. As the incendiary composition comprises lesser amounts of paraffin wax, such as 5 weight percent to 10 weight percent, the flame temperature increases. As the incendiary composition comprises less polytetrafluoroethylene, such as from 20 weight percent to 30 weight percent, the reaction energy increases.